6.2 Blood System

Heart Structure

❤ Two sides; left and right double circulation; systemic and pulmonary

❤ each side; a ventricle - pumps blood out into arteries an atrium - collects blood from veins and pass to ventricle

❤ each side; atrioventricular valve between atrium & ventricle , semilunar valve between ventricle and artery

❤ oxygenated blood flows into left side through pulmonary vein from lungs and out through aorta

❤ Deoxygenated blood flows into right side of heart through vena cava and out through pulmonary artery

Arteries

⭐ convey blood at high pressure from the ventricles to tissue of body

✅ Both elastic and muscle tissue; toughness of walls - withstand high blood pressure (without bulging outwards; Aneurysm)/bursting

✅ Elastic tissue contains elastin fibres which store energy that stretches them at peak of pumping cycle

✅ Contraction of smooth muscle in artery wall determines diameter of lumen and rigidity of arteries, controlling overall flow through them

✅ Blood's progress in arteries is pursatile, not continuous. Pulse reflects each heartbeat (wrist&neck)

✅ Each organ of body is supplied with blood by one/more arteries. (e.g: Kidney with renal artery, Liver w hepatic artery, Heart w coronary arteries)

⭐ Artery walls ; composed of three layers:-

🏴 Tunica externa - a tough outer layer of connective tissue

🏴 Tunica media - a thick layer containing smooth muscle and elastic fibres made of the protein elastin

🏴 Tunica intima - a smooth endothelium forming the lining of artery

⭐ Arterial blood pressure

🚩 The peak pressure reached in artery is called systolic pressure - pushes the wall of artery outwards, widening lumen. stretching elastic fibres, & storing potential energy

🚩 end of heartbeat, pressure falls - elastic fibres squeeze blood ; diastolic pressure

🚩vasoconstriction - lumen is narrowed, high BP vice versa vasodilation

Veins

⭐ Veins collect blood at low pressure from the tissues of the body and return it to the atria of the heart

✅ fewer muscle and elastic fibres

✅ can dilate to become much wider to hold more blood

✅ Blood flow is assisted by gravity and by pressures exerted on them by other tissues especially skeletal muscles

✅ Contraction makes a muscle shorter and wider so it squeezes on adjacent veins like a pump (e.g: walking, sitting - improves venous blood flow)

✅ Each part of the body is served by one/more veins (e.g: subclavian veins, jugular veins) [hepatic portal vein does not carry blood back to heart, but from stomach to liver]

⭐ Valves in veins and the heart ensure circulation of blood by preventing backflow

❤ To maintain circulation, veins contain pocket valves ; three cup-shaped flaps of tissue

❤ If blood starts to flow backwards, it get caught in flaps of pocket valve, which fill with blood, blocking the lumen of the vein

❤ When blood flows towards the heart, it pushes the flaps to the sides of the vein. Pocket valve opens and blood flow freely

❤ Blood flows in one direction only and make efficient use of contraction of muscles

⭐ Blood flows through tissue in capillaries with permeable walls that allow exchange of materials between cells in the tissue

✅ diameter of 10 micrometer

✅ branch and rejoin repeatedly to form capillary network

✅ transport blood throught all tissues except in lens and cornea in eyes

✅ consist of one layer of endothelium cells, coated by a filter-like protein gel, with pores between cells (only tunica intima)

✅ close to active cells in tissues

✅ allows plasma to leak out and from tissue fluid

✅ permeability differ between tissues, enabling particular proteins and large particles to reach certain tissues